Membrane free liquid metal batteries for grid scale energy storage

Solar and wind power are renewable and green power sources that are seeing huge investments at the time. Weather dependence is the biggest challenge for this type of energy, as the energy needs and production opportunities does not always overlap. However due to the high cost of batteries today, investments in grid scale storage solutions is not economically viable. In order to be able to store energy in such large amounts that it can have an impact on the grid balance, new and cheaper solutions than current battery technology have to be developed. Our concept goes all the way back to basics and focuses on creating simple solutions based on chemical reactions that can take place in cheap materials in order to save cost. In the first two years of the project a post doc candidate, Junli Xu, worked in the project as a part of NTNU's contribution, she worked in close collaboration with SINTEF researchers. The focus in the first stage was to study candidate materials for construction of the battery, and to assess prices and availability of these materials. During these years more than 10 battery experiments were run, in addition to pure characterization experiments. A solid foundation of knowledge to asses the possibilities and limitations were formed. The results gave two manuscripts, that now have been published. In 2016 we got approval to continue to the second phase of the project after the mid term evaluation. We are now been working in the second phase for more than one and a half year. Our focus here has been to prove the principles from phase one with the new materials. One continuous challenge have been the vapor pressure of liquid Na, and we investigated numerous design variations to best contain the liquid Na at these temperatures. We foresee that the sealing of the battery with focus to remove voids will be easier with scaling. Another important focus area has been to establish international contacts. There are some, but few, other research organist ions that are working within this field, and to establish collaboration is important in order to share focus areas, and to consider collaboration in international research programmes. We had already knowledge about MIT and Donald Sadoways research. We arranged a workshop in Trondheim in September 2017, where we got 38 visitors from 9 different countries, 7 European, Japan and USA. Professor Donald Sadoway came and held the opening lecture with the title " High Temperature Batteries for Stationary Energy Storage". This workshop gave us several new contacts to researchers working on different large scale battery technologies which is important for us with regards to establish future EU-proposals. The work within this project gave us much new knowledge, and some very good and promising results that we can bring in and continue to build on in new projects. At the moment we are aiming on getting these activities in at least one EU-funded project, where we will have the chance to collaborate with skilled researchers all across Europe.

Large scale energy storage is becoming progressively more important for grid balancing with the increased use of renewable energy sources such as wind, wave and solar in the European power grid. The new energy sources have a more unpredictable power outpu t than conventional power plants and hence require very flexible and efficient energy storage systems. Currently, there are several technologies suggested for large scale energy storage including pumped storage hydroelectricity, hydrogen, flywheels and va rious types of batteries but each have their specific limitations and drawbacks and are not applicable in every situation. Today none of the existing technologies can offer sufficient flexible storage at an affordable price. Liquid metal batteries can pr ovide such as a solution due to their very high current density if the cost of production can be reduced and the safety significantly improved. Therefore, in this project, we will revive research in the area of liquid metal batteries by the introduction of the novel concept of producing a "membrane-free" molten salt battery. The exclusion of the brittle, expensive beta-alumina ion selective membrane and its replacement with a cheap durable diaphragm material will significantly improve both performance a nd reduce the cost level of liquid metal batteries. Furthermore, the choice of tailored electrolytes and electrodes will ensure a safe battery system, which in the unlikely event of mechanical failure will discharge without any undesired effects such as fire or explosion. In addition, the electrolyte, electrodes and diaphragm material chosen are relatively abundant, cheap materials with low environmental impact. The successful implementation of these new concepts to the liquid metal battery will result i n a system which is considerably cheaper to produce, has higher current density and is a substantially safer than current molten battery systems.